Dockerfile: Rebase etcd image to debian

[wenjiaswe]

To improve security and maintenance effort for etcd releases, it would
be ideal to rebase etcd base image from Alpine to Distroless. However,
note that distroless images by default do not contain a shell, etcd still has
shell scripts in https://github.com/etcd-io/etcd/tree/master/hack, I will
first rebase to Debian in v3.4.

This work is still in progress, open now to unveil any unexpected errors
from testing.

Fixes #10804

/cc @yuwenma

[codecov-io]

Codecov Report

Merging #10805 into master will increase coverage by 2.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10805      +/-   ##
==========================================
+ Coverage   62.93%   64.97%   +2.03%     
==========================================
  Files         400      401       +1     
  Lines       37646    39258    +1612     
==========================================
+ Hits        23694    25508    +1814     
+ Misses      12343    12112     -231     
- Partials     1609     1638      +29

Impacted Files	Coverage Δ
proxy/grpcproxy/register.go	69.44% <0%> (-11.12%)	⬇️
clientv3/balancer/grpc1.7-health.go	46.22% <0%> (-5.82%)	⬇️
raft/rawnode.go	71.02% <0%> (-4.71%)	⬇️
pkg/adt/interval_tree.go	86.78% <0%> (-3.31%)	⬇️
raft/status.go	57.37% <0%> (-2.15%)	⬇️
raft/progress.go	93.71% <0%> (ø)
etcdmain/config.go	82.97% <0%> (+0.08%)	⬆️
etcdserver/api/rafthttp/transport.go	84.58% <0%> (+0.41%)	⬆️
mvcc/backend/batch_tx.go	58.37% <0%> (+0.6%)	⬆️
etcdserver/api/v3rpc/watch.go	79.08% <0%> (+0.65%)	⬆️
... and 33 more

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[wenjiaswe]

cc @jingyih @hexfusion would you please take a look? Thanks!

[jingyih]

I think this was brought up during last community meeting and people agreed to make this in v3.4. I am adding the 3.4 milestone for now. Please let me know if I remembered incorrectly.

cc @gyuho

[gyuho]

lgtm

@wenjiaswe @jingyih Can we highlight this in changelog 3.4?

[wenjiaswe]

@gyuho thanks! I am working on the change log

[BenTheElder]

@wenjiaswe will this move to distroless later?
if not, how can we keep this in sync with the upstream debian-base?